To date, polyurethane is one of the best performing products. It allows you to attain a high R-value in a narrow spacing. It also acts as an air and vapour barrier. As regards thermal roofs, polyisocyanurate panels are among the most efficient on the market.
The insulation requirements vary depending on the building system. It is suggested to consult the description sheet to know the R-value of the insulation. The data may vary in case of a rooftop terrace or green roof.